This invention relates generally to spectroradiometry and specifically to telescopic spectroradiometry.
In monitoring a two-dimensional region of the earth from an aircraft or spaceship, such as a satellite, it is desirable to obtain an image of radiation from that region in at least two different spectral wavebands. Thus far, such spectral data has been gathered using primarily two different types of systems: photography and point-by-point scanning.
Photographic systems require the user to photograph the entire region utilizing an optical filter for a first spectral waveband and then to photograph the entire region again, this time using an optical filter for a second spectral waveband. Each time a photograph is taken, data for a single spectral waveband is gathered for the entire two-dimensional region simultaneously. In other words, data for a given waveband is gathered at one time for a wide field of view. After all photographs have been taken, they must be processed and then the data from each photograph must be correlated. Results are not available in real time, but rather require lengthy photographic processing and correlation of the information contained in the various finished photographs.
Scanning systems, on the other hand, build up an image from a scan of consecutive points and lines according to a predetermined scanning pattern. Light from the two-dimensional region being scanned is coupled through a small aperture to a spectroradiometer which analyzes the spectral content of radiation from the entire region on a point-by-point basis. The instantaneous field of view must be small because spectroradiometers require a small input aperture and because a large field of view results in a loss of spatial resolution. As the field of view scans the entire two-dimensional region point-by-point within each line of the region and line-by-line within the entire region, the spectroradiometer is continuously separating light incident from the scan into its spectral components.
Presently utilized scanning systems require elaborate mechanical mechanisms for the precise point-by-point scanning required. Such mechanisms require a great deal of attention for alignment, maintenance, etc.
Because each of these different types of remote sensing systems has operational limitations, it is desirable to have available an optical instrument for gathering two-dimensional spectral scene information that is compact, lightweight, has low power requirements, and requires minimal attention.